For the existing LED decorative bulb, a tail electrode of a screw-on lamp holder at the tail thereof is opened with a small hole, so that a conductive pin inside is extended out, and then is connected with the tail electrode by soldering tin. For convenience in connection by soldering tin and connection reliability, this small hole has to be provided, so that the center of the tail electrode is opened with such small hole used for electric connection. However, it is because of the small hole that the waterproofness of the LED decorative bulb becomes a problem. In order to make it waterproof, the previous method is to process the small hole in the conductive pin and the tail electrode in enclosed type connection by soldering tin to achieve the object of waterproofness; however, such processing result often makes the waterproofness below the required due to the existing defects of soldering tin, as well as heat expansion and cold contraction, loosening of soldering tin and a series of factors. Therefore, it is necessary to develop a new waterproof LED decorative bulb to overcome these above deficiencies.